Added Vec2d, Vec3d and Vec4d classes, and remapped Vec2, Vec3 and Vec4 to

Vec2f, Vec3f an Vec4f respectively, with typedef's to the from Vec* to Vec*f.

include/osg/Drawable

@@ -22,9 +22,9 @@
 
 namespace osg {
 
-class Vec2;
-class Vec3;
-class Vec4;
+class Vec2f;
+class Vec3f;
+class Vec4f;
 class UByte4;
 class Geometry;